Only about ten to fifteen percent (10-15%) of multi-organ donors have lungs that are suitable for transplantation and the resulting organ shortage is a well-known problem. Pulmonary edema contributes to donor organ inviability and may be caused by an increase in vascular pressure or an increase in capillary permeability. Vascular pressure increases are the result of pump failure (cardiogenic), volume infusion, and vasopressor use to maintain hemodynamic stability and organ perfusion. Increased capillary permeability is due to the release of inflammatory mediators and is well documented in brain death.
The lymphatic system includes a network of vessels generally separate from veins and arteries. Rather than whole blood, the lymphatic vessels carry lymphatic fluid (or lymph). The lymphatic system serves a variety of physiologic purposes, including returning interstitial fluid to the vascular space, transporting fats from the digestive tract, and transporting immune-mediating cells. The composition of lymphatic fluid is similar to plasma. It contains white blood cells, but generally does not contain red blood cells, platelets, or various other components of whole blood. The lymphatic system culminates in a single large channel called the thoracic duct, which joins the central venous system at the confluence of the left internal jugular and subclavian veins.
Historically, the lymphatic system has been directly accessed rarely in medical procedures. For example, some diagnostic procedures involve direct cannulation of peripheral lymphatic vessels, e.g., to infuse dye for identification of lymph nodes. Direct access of the central lymphatic vessels, such as the thoracic duct, is generally avoided. For example, a defect created in the thoracic duct generally does not readily close on its own, leading to significantly morbid conditions, such as chylothorax (persistent collection of lymphatic fluid around the lungs).
The lymphatic system does, however, eventually drain into the vasculature. A majority of lymphatic vessels come to a confluence in the thoracic duct which generally enters the venous system at the junction of the left subclavian vein and the left internal jugular vein. A series of valves generally facilitate one-way flow of lymphatic fluid into the venous system and prevent reflux of whole blood into the thoracic duct. Although not well studied, disruption of one or more of these valves may have negative consequences. Therefore, it may be desirable to protect these valves and/or the lymphatic vessels themselves from damage.
Under normal circumstances, the lung lymphatics absorb excess interstitial fluid and prevent alveolar fluid accumulation. In pulmonary edema, the lymphatic system is overwhelmed or ineffective as vascular pressure prevents forward flow or alveolar migration increases with membrane permeability.
Accordingly, reducing downstream pressure and/or increasing outflow from the lymphatic system may have a positive effect on pulmonary edema and limit the fluid accumulation in the lung. Such an approach has not been viable clinically, as thoracic duct cannulation historically has required an open surgical approach and irreversible transection of the distal duct.